San Francisco 49ers running back Frank Gore takes off his gloves after sparring with Brian Schwartz, his trainer and the owner of Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

Photo: Sarah Rice, Special To The Chronicle

San Francisco 49ers running back Frank Gore takes off his gloves...

Image 2 of 7

San Francisco 49ers running back Frank Gore spars with Brian Schwartz, his trainer and the owner of Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

Photo: Sarah Rice, Special To The Chronicle

San Francisco 49ers running back Frank Gore spars with Brian...

Image 3 of 7

San Francisco 49ers running back Frank Gore sits in the hypoxic training dome, where oxygen has been removed to resemble 10,000 feet, as part of his training routine at Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

Photo: Sarah Rice, Special To The Chronicle

San Francisco 49ers running back Frank Gore sits in the hypoxic...

Image 4 of 7

Gore, sparring with trainer Brian Schwartz, says the gym's real boxers are surprised by what he shows in the ring.

Photo: Sarah Rice, Special To The Chronicle

Gore, sparring with trainer Brian Schwartz, says the gym's real...

Image 5 of 7

San Francisco 49ers running back Frank Gore spars with Brian Schwartz, his trainer and the owner of Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

Photo: Sarah Rice, Special To The Chronicle

San Francisco 49ers running back Frank Gore spars with Brian...

Image 6 of 7

San Francisco 49ers running back Frank Gore spars as part of his training routine at Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

Photo: Sarah Rice, Special To The Chronicle

San Francisco 49ers running back Frank Gore spars as part of his...

Image 7 of 7

San Francisco 49ers running back Frank Gore spars as part of his training routine at Undisputed Boxing Gym in San Carlos, Calif., on Saturday, June 28, 2014.

"When I see the hole, I go get it," Gore says, clearly enjoying himself.

Gore is 31, heading into his 10th season with the 49ers, his ninth as the bell cow, the spiritual leader of the offense. For the past three years, Gore has trained in the offseason at Schwartz's Undisputed Boxing Gym in San Carlos.

Michael Crabtree turned Gore on to Undisputed. Crabtree went there during his holdout before his rookie season. He brought Gore there three years ago.

The first time Gore got into the ring to hit with Schwartz, he quit before the end of the first round. Now he goes 15 rounds, hard.

Gore is sweating like a lawn sprinkler, and beaming.

"What's our motto?" a ringsider says to Schwartz.

"If it's not fun, don't do it!" Schwartz says.

The ringsider is Victor Conte, infamous for his role in the BALCO scandal and Olympian misdeeds, but working the honest side of sports training and nutrition since he did four months in the slammer in 2005 and '06.

It's an odd mix, these four guys, thrown together by fate and chance encounters. Crabtree found Undisputed because the wife of one of his accountants worked out there.

Conte came into the picture four years ago, after meeting boxing champ Nonito Donaire in a bank. The bank manager introduced the two and they talked shop. Turns out that Conte's daughter Veronica, who runs his nearby business, SNAC (Scientific Nutrition for Advanced Conditioning) System, works out with Donaire's conditioning coach. Small world.

But Conte can sell a program and Schwartz is open-minded, and soon Conte was supplying Donaire and the other fighters with blood testing and supplements, and moving them into super-high-tech training.

Conte designs workout protocols and testing and supplement programs.

"We didn't know anything about this stuff until Victor came along," Schwartz says.

Crabtree fell into step, and soon Gore joined the party. He has embraced the boxing aspect, sometimes sparring with Schwartz and other fighters. Crabtree recently started doing some ring work, though not sparring.

"Mentally, boxing is like being a running back," says Schwartz, a former world champion in karate and kickboxing. "You're getting ready to go to war, to get hit."

Now the action moves from the canvas ring to a giant plastic igloo. This is Conte's new baby, the SNAC Altitude Dome, an air-tight, transparent plastic dome 12 feet high and 18 feet in diameter. Low-oxygen air is pumped in.

Conte, a mad scientist, designed the dome and had it built in China for $35,000. Athletes train in short bursts, at the equivalent of two to three miles above sea level.

"I hate this," Gore says, climbing into the igloo.

The dome is large enough for equipment, like treadmills and stationary bikes, and for sparring - hypoxic boxing.

"This helps with reaction time, concentration and focus, oxygen utilization and energy," Conte says of the ring work inside the dome.

Gore and Schwartz are dancing. During these oxygen-deprived bursts, Gore's heart rate soars as high as 205 beats per minute. He says he notices that between plays in games and scrimmages, when everyone else is bent over, hands on knees, gassed, he's standing up, fresh and ready to rip.

When Gore started working out there, he was coming back from a serious hip injury. In three seasons, he has not missed a game and has gained at least 1,100 yards per season, despite the handicap of an offense that provokes defenses to stack the box.

Along with his eight-week offseason program there, Gore drops in a couple of times each week during training camp for workouts and to watch the boxers. During the season, twice a week Gore and Crabtree climb into the hyperbaric chamber, which supposedly speeds healing. There is talk of near miracles, like a boxer's black eye disappearing almost overnight after a chamber session.

Conte designs supplement packets for Gore and Crabtree - powders, pills, soft gels and sublinguals - to take before a game and at halftime. Justin Smith, Bruce Miller and two or three other 49ers, also get custom-formulated packets.

"If I don't have it, I get nervous," Gore says. "I make sure before I leave for the game or get on the plane that I have (the package) in my bag."

His workout over, Gore finally sits down.

"It helps you get your mind right," Gore says, nodding to the ring. Boxing "is a mind thing, and also a challenge. I'm very competitive."

Of his sparring sessions with the real boxers, Gore says, "B (Schwartz) don't let 'em go all out. He wants me to be safe, but I think I do a pretty good job. I know when I'm done, all the true boxers (are) surprised at what I know."

Gore mentions that someone recently told him he was about 1,000 yards behind Jim Brown on the all-time rushing list. (Actually he's 2,345 behind Brown.) Gore says he has goals, and enthusiasm.

"I still love it, man. I love it!"

Gore is entering the last year of his contract.

"I would love for (the 49ers) to bring me back here," he says. "If they don't, I just take my business somewhere else. I still love it. That's my goal, is to walk away when I want to walk away."

I mention that his teammate Vernon Davis is more vocal about his contract, going on a national media tour to enlist public support for his demands, even though his current contract has two more seasons.

"What's Vernon doing?" Gore asks with genuine curiosity, not scorn.

I say that it seems like Davis is enjoying the national attention.

"I don't like attention," Gore says.

But he gets attention, quietly. When training camp opens, the 49ers' bell cow will be leading the herd. He won't be grabbing a knee.

Conte, fittingly, believes in 2nd chances

Victor Conte knows that some people forgive, some forget, some do neither.

"There are people who think you should burn in hell," Conte says. "There are people who do not want the association" with his name or services.

But he has assembled a training stable of athletes, mostly boxers, including six who hold or have held world championship belts. He heads the SNAC Boxing Team, providing training, testing and supplements.

"They do get (drug) tested," Conte says of his athletes. "I would say anybody working with me becomes a target. (Phillies outfielder) Marlon Byrd used to get tested about five times a season. The first season he worked with me he was tested 11 times."

Conte believes in second chances. His athletes sometimes do track work with Remi Korchemny, who was banned from track for life during the doping scandals.

Conte offers to share his juicing expertise with groups that fight drugs in sports like the World Anti-Doping Agency, but says his advice is largely ignored.

"I do not believe they have genuine interest in catching people," Conte says. "It's all about propaganda."